A gas turbine generally comprises a compressor, a combustor, and a turbine, wherein the compressor provides compressed air generated by a plurality of compressor blades to the combustor, the compressed air is combusted with fuel in the combustor to generate hot gas, and the hot gas is provided to the turbine such that a plurality of turbine blades turn. The surface temperature of the plurality of turbine blades becomes very high due to the hot gas passing through the turbine blades, and the hot temperature of the turbine blades causes coating spallation and oxidation of the turbine blades. In addition, as a result of the hot surface temperature, a platform of the turbine blades tends to bow and becomes weak due to cracking. Thus, in the conventional design, a serpentine cooled turbine is used in such a manner that coolant passes through the inside of the turbine blades in order to lower the temperature. However, the temperature of the turbine blades is not decreased efficiently enough to sufficiently inhibit the coating spallation and cracking.